I disagree with the election part, but agree nevertheless with your viewpoint. Every country has a constitution (written, otherwise, under transition or whatever— ours is the most potent in acceptance), but every place can be overwhelmed in the short term and need practical accommodation, which is basically what is going on. Z’s problem is not illegitimacy, but impotence.
The whole thing was a little theatre-staged, so I try think of why. It’s obviously pre-negotiation puffery. Could it even be that Zelenskyy knows realistically that he has to give up something important (and will) but needs a public demonstration—with his own people as the audience—that he was as tough as he could be and went down swinging trying to get more? Ie, trying to avoid being considered the traitor in his own country who agreed to unequal terms after losing the war. So they stage him being told, and the world hearing it in real time, that he does not have the cards to make a better deal.
Just a theory: Trump says, “I’ll be the bad guy and cover for you with your base.”